Chromium plating from baths catalyzed with alkanedisulfonic-alkanesulfonic compounds with inhibitors such as aminoalkanesulfonic acids and heterocyclic bases

Abstract

 C1-C18 Alkylsulfonic or Alkyldisulfonic compounds and Aminoalkilsulfonic acids or salts thereof, are used as additives in chromium plating baths to reduce anodic corrosion, improve the covering and penetrating power of the bath, reduce the surface-tension and give a bright deposit.

Description

[0001] The present invention relates to chromium plating baths with organic additives, resistant in solutions of chromium, to obtain electrodeposition of penetrating and covering chromium while avoiding anodic corrosion. Alkane sulfonic and disulfonic acids were first used as additives for electrolytic baths in 1930, at the Politecnico of Milan.

[0002] After the Second World War American, French, German, Polish and Soviet researchers reported and claimed disulfonic acids and their salts as improvers of cathode efficiency in chromium plating baths. However, application of these types of baths on a large scale over a period of time revealed inferior properties compared to traditional baths, in that they cause accelerated corrosion of the anode (an alloy of lead).

[0003] The mechanism that leads to these drawbacks is described as follows:

[0004] Acidic dissolution of PbO₂ due to the polarization of acid concentration:

        PbO₂+2H⁺ = PbO²⁺+H₂O

[0005] Reaction of the lead oxide favored by the excess of acidity with H₂O₂ formed at the anode

        PbO₂+H₂O₂+2H⁺ = Pb²⁺+O₂+2H₂O

(the reformation and the stabilization of the PbO₂ is, on the contrary, favored by a deficit of free acid: Pb²⁺+ O₂+ H₂O= PbO₂+ H₂O₂+ 2H⁺).

[0006] The anode degradation rate is further increased by the fact that the Pb²⁺ ions formed are removed from the equilibrium by the formation of stable complexes with ions in solution - for instance traces of halides and degradation products of the organic acids.

[0007] Many proposals have been suggested to eliminate the drawbacks described above, by chemical and electrical means, but with unsatisfactory results.

[0008] This patent claims the use of certain additives in specific concentrations, to improve the covering and penetration power of the chromium plating baths while avoiding anodic corrosion.

[0009] Anodic corrosion can be drastically reduced or eliminated by adding appropriate concentrations of aminoalkylsulfonic compounds or heterocyclic bases to the chromium plating baths containing Alkyldisulfonic or Alkylsulfonic acids or salts.

[0010] These substances in elevated concentrations can lead to a cathode efficiency below that of a traditional chromium plating bath.

a) The aminoalkylsulfonic and the heterocyclic bases are added to the chromium plating baths containing Alkyldisulfonic and Alkylsulfonic acids and salts, in such concentrations as to give a Faraday output of 15-16% constant (not of interest in this patent which claims other parameters).

b) The corrosion inhibitors, chemical compounds, added to the chromic solutions containing Alkylsulfonic and Alkyldisulfonic acids and salts, drastically reduce the corrosion rate of anodes immersed in them, shifting the corrosion potential to values nobler than the primary potential, or increasing the overload of the anodic or cathode process or of both simultaneously according to their chemical nature.

[0011] Such purpose is achieved by the present invention, which relates to chromium plating baths comprising one or more compounds having general formula:

        X - (CH₂)_n- SO₃H     [1]

where:

n= integer from 1 to 18

X= NH₂

and salts thereof,
and/or nitrogen containing heterocyclic bases such as C₅H₅N or its homologues.

[0012] In presence of these compounds the anodic corrosion is drastically reduced even in the presence of high concentrations of compounds of general formula:

        Y - (CH₂)_n- SO₃H     [2]

where:

n= integer from 1 to 18

Y = H or SO₃H;

and salts thereof.

[0013] These additives are employed in chromium plating baths, in combination with the compounds of general formula of Type [1], to give penetrating and covering chromium deposits without corrosion of the lead alloy anode.

[0014] The invention therefore also relates to chromium plating baths according to Claim 8. Preferential aspects of the invention are claimed in Claims 9-11.

[0015] Another object of the invention is a concentrated formulation containing CrO₃ and one or more additives of formula [1] and/or [2] for the preparation of chromium plating baths, according to Claim 12.

[0016] Further objects of the invention are the uses of the compounds of formula [1] and [2] according to Claims 13, 14 and 15.

[0017] A further advantage of the present invention is given by the fact that the addition to a chromium plating bath of compounds of general formula [1] and [2] with 6-8 atoms of carbon, leads to a reduction of the surface tension of the bath with the advantage of eliminating splashing, reducing the losses to transport with notable saving of chromic acid, so much so that their employment is cost-reducing and improves the work environment (TLV-TWA values).

[0018] Another object of the invention is thus the use of the compounds of formula [1] and [2] according to Claim 16.

[0019] Penetrating power is a grading of the metal in function of the electric current, where chromium plating baths have scarce penetrating power.

[0020] Various methods for the measurement of the penetrating power of the electrolytic baths exist as for instance:

a) the technique of E.Haring and W.Blum;

b) Method of C.Pam.

[0021] The invention will now be illustrated by way of non-imitative reference to the following examples and to the enclosed drawings, where:

• Figure 1 is the schematic representation of a test-plate of the penetrating power of a traditional bath.
• Figure 2 is the schematic representation of a test-plate of the penetrating power of a traditional bath in the presence of additives, not limiting.
• Figures 3 and 4 are the schematic representation of the covering power of a V-shaped plate in a traditional bath.

[0022] We have established the penetrating power of the chromium plating bath through a Hull cell. For this purpose it is sufficient to observe the presence and degree of deposition of chromium which is obtained on the test-plates in zones of least density of current.

EXAMPLE 1

[0023] A chromium plating bath of the traditional type was prepared :

250

gr/ lt CrO₃

2.5

gr/ lt H₂SO₄

[0024] The chromium was deposited in Hull cell, for 8' on an iron cathode of length of 10 cm, at a temperature of 60°C with current of 10 Amp.

[0025] The bare part was 6 cm.

EXAMPLE 2

[0026] The test was repeated, in similar conditions to Example 1, in the presence of non-limiting additives:

250

g/lt CrO₃

2.5

g/lt H₂SO₄

6

g/lt Ethanedisulfonic sodium salt

1

g/lt Aminoethanesulfonic acid

[0027] The bare part was 2 cm.

[0028] Covering power of a chromium plating bath is the minimum current at which the chromium deposit begins to form.

EXAMPLE 3

[0029] A chromium bath of the traditional type was prepared:

250

g/lt CrO₃

2.5

g/lt H₂SO₄

[0030] The cathode used was a V-shaped panel. Temperature was 60°C.

[0031] The chromium was deposited on the cathode for 8' with a current of l0 Amp.

[0032] The part not electroplated was 6 cm. (fig. 3).

EXAMPLE 4

[0033] The test is repeated with a catalyzed chromium plating bath in the following concentrations:

250

g/lt CrO3

2.5

g/lt H2SO4

6

g/lt Ethanedisulfonic sodium salt

1

g/lt Aminoethanesulfonic

[0034] The part not electroplated was of 3 cm. (fig. 4).

[0035] The chromium plating baths were re-tested in the presence of nitrogen containing heterocyclic base-type inhibitors; the results were similar to the preceding examples.

[0036] Figure 3 is a scheme of "V"-shaped cathode after deposition in a traditional bath for evaluation of the covering power.

[0037] Figure 4 is an analogous scheme to that of figure 3 after deposition in a bath containing the additives according to the invention.

[0038] The salts of the alkyldisulfonic acid can be prepared by reaction of an Alkyl dihalide with a sulphite, through a nucleophillic substitution reaction with the halogens, the leading groups, that are replaced by SO₃ groups. The alkyl dihalides that can be employed in this process have general formula:

        C_nH_2nX₂

where

n = integer from 1 to 18

X= Cl, Br, I

e.g. 1,2-dibromoethane, 1,3-dibromopropane, 1-chloro-3-bromopropane etc.

[0039] The reactivity order is I > Br > Cl; the more convenient compounds are the Alkyl dibromides, e.g. 1-2 dibromoethane - a good compromise between reagent cost and reactivity.

[0040] Water-soluble sulphites e.g. Na₂SO₃, K₂SO₃, (NH₄)₂S0₃, ZnSO₃, MgS0₃ etc. can be used as reactive sulphites, or the corresponding soluble metabisulphite could be used, treated with an equimolar quantity of the corresponding hydroxide.

[0041] Water or H₂O-ethanol, H₂O-methanol mixtures can be used as solvents. The reaction proceeds very slowly at ambient temperature and T > 80°C is preferable to give an acceptable reaction.

[0042] The reaction can be represented by the following general equation

where n = number from 1 to 18, X = Cl, Br, I.

[0043] The reaction must take place with sulphite in excess of the stoichiometric quantity to guarantee the maximum yield of alkyldisulphonate and minimize the secondary reactions of hydrolysis of the halide, with formation of glycols and hydroxyalkylsulphonates.

[0044] The reaction can be performed with a sulphite : dibromoethane molar ratio of from 1.1/1 to 1.5/1.

Example 3 (not limiting)

[0045] A solution formed of:

376 g. Na₂SO₃

1 liter H₂O

is placed in a 2 liter reactor provided with refrigerant thermometer, stirrer and drip-funnel.

[0046] This solution is heated to a temperature of 80°C; thereafter, 200 g of dibromoethane was added over 40 minutes; the molar ratio of sulphite/dibromoethane is 1.4 compared to the stoichiometric equivalent. The reactor was left to reflux for 6 hours.

[0047] The yield of the reaction is 95%.

Example 4

[0048] The procedure is the same as in the preceding example; the reagent proportions are the following:

161 g.

Na₂SO₃

100 g.

dibromoethane

450 g.

H₂O

[0049] The molar ratio sulphite/ dibromoethane is 1.2 compared to the stoichiometry. The yield of the reaction is 9l% of the theoretical.

[0050] The reaction product can be separated from the sodium bromide, the unreacted sulphite and the by-products by means of recrystalization in water or in aqueous-methanol.

[0051] The methodology is also similar for dihalides or Alkyl halides, but, obviously, the molar ratios must be adjusted accordingly.

Claims

1. An electrolytic chromium plating process containing the additives specified in concentrations from 1 to 20 g./lt.

2. An electrolytic chromium plating process containing the additives specified to prevent anodic corrosion in concentrations from 1 to 10 g./ lt.

3. An electrolytic chromium plating process containing the additives specified to lower the surface-tension of the chromium solution.

4. An electrolytic chromium plating process containing the additives specified to improve the covering power.

5. An electrolytic chromium plating process containing the additives specified to improve the penetrating power.

6. A method of preparation and production of the compounds cited in general formula in this Patent.

7. The application in chromium plating baths of the compounds cited by the Patent in general formula and also their method of production.

8. A chromium plating bath, characterized by comprising one or more compounds selected from compounds of general formula:

        X-(CH₂)_n-SO₃H     [1]

where:

n = integer from 1 to 18

x = NH₂

and the salts thereof;
and heterocyclic nitrogen containing bases such as C₅H₅N and its homologues.

9. A chromium plating bath according to claim 8, further comprising one or more compounds of general formula:

        Y-(CH₂)_n-SO₃H     [2]

where:

n = integer from 1 to 18

Y = H or SO₃H

and the salts thereof.

10. A chromium plating bath according to claim 8 or 9, comprising one or more compounds of formula [1] and/or [2] having from 6 to 18 atoms of carbon, or the salts thereof.

11. A chromium plating bath according to any previous claim, wherein said additives are present in total concentration whitin the range of 1to 20 g/lt.

12. A formulation for the preparation of a chromium plating bath according to any Claim 8 to 11.

13. The use of compounds having general formula:

        X-(CH₂)_n-SO₃H     [1]

where:

n = integer from 1 to 18

X = NH₂

or salts thereof,
and of heterocyclic nitrogen-containing bases such as C₅H₅N and its homologues, to reduce or prevent anodic corrosion in chromium plating baths.

14. The use of compounds having general formula:

        Y-(CH₂)_n-SO₃H     [2]

where:

n = integer from 1 to 18

Y = H or S0₃H

or salts thereof,
to improve the penetrating and covering power in a chromium plating baths.

15. The use of compounds having general formula

        X-(CH₂)_n-SO₃H     [1]

where:

n = integer from 1 to 18

X = NH₂

or of the salts thereof, and of heterocyclic nitrogen-containing bases such as C₅H₅N and its homologues, in combination with compounds of general formula

        Y-(CH₂)_n-SO₃H     [2]

where:

n = integer from 1 to 18

Y = H or SO₃H,

or salts thereof,
to improve the penetrating and covering power of a chromium plating bath.

16. The use according to the Claim 14 or 15, wherein Y is a sulfonic acid group or a salt thereof.

17. The use of compounds having general formula:

        X-(CH₂)_n-SO₃H     [1]

where:

n = integer from 6 to 18

X = NH₂

and salts thereof,
and of compounds having general formula:

        Y-(CH₂)_n-SO₃H     [2]

where:

n = integer from 6 to 18

Y = H or SO₃H

and salts thereof, to lower the surface-tension in chromium plating baths.

Drawing